Enable Collision for multiple objects
Here's a quick python script to add the collision modifier for all selected objects. Just select all the objects to be made into collision objects and run the script, script is not at all optimized as it is using bpy.ops, so anything above 300 objects might take 1 or 2 secs to apply.
import bpy
for i in bpy.context.selected_objects:
     bpy.context.view_layer.objects.active = i
     bpy.ops.object.modifier_add(type='COLLISION')